how strong do the wireless need to be?

Im getting a new comp and everything, and im going to move my comp upstais. My modem and router are both down stairs though.I was wondernig what kind of adapter do i need, and do i need to get a ner router? because at the shop, the man kept saying i needed a more expensive adaptor and router becuase the signal needed to be strong to get through the walls. I have a netgear WGR614 whic use the 802.11g signal. would the adaptor, also from netgear, the WG311 be enough?

Curiosity was framed. Stupidity killed the cat.
(i know it has nothing to do with comps, but i think its funny ^^" )

You'll know if it is enough when you get it home and try it. Bottom line. Nobody knows what your wireless environment is. You can however get advice on what has worked well for others. Unless you have rebar in your walls or something like a refrigerator directly in the path you'll "probably" be fine.